How to wiggle multiple keyframed objects with Animation Nodes
You will have to put these nodes into a loop to use the effect on multiple objects. To get different motions for every object you have to link the Index output of the Loop Input node with the Seed input of the Wiggle Vector node.



Make sure that you disable "Use Current Transforms" in the Object Transforms Input node. Otherwise the objects will move away when you stop the playback. You find the setting in the advanced node settings panel on the right.

The basic idea here is that you evaluate the fCurve to get the location the cube would normally have (the Transforms Input node does that). Then you create an additional vector that wiggles around the origin with a maximum amplitude (0.5 in the image above).

By adding both vectors together you get an offset on top of the original keyframed position.
The last node sets the new location on the object and overwrites the keyframed position.